For #Meta that makes it substantially easier to moderate for the #Fediverse: They only have to keep an eye on accounts, that opted-in to the federation. (Of course, only if they even want to moderate)
For people (say some journalists), who like #Mastodon and the #Fediverse, but who miss some or large parts of the former user base of #Twitter, this will create an incentive to migrate to #Threads even. There, they have potentially all connections.